Summer Session II Limnology Report: Bear Lake

Bear Lake Township, Kalkaska County, MI.

Zach McDonald (Covenant College) & Jessica Hartum (Kings University) Au Sable Institute of Environmental Studies

Introduction

Bear lake is a 316-acre glacially formed lake in Kalkaska County, Michigan that

lies within the Manistee River watershed. Bear lake is a well developed lake with

residences covering the circumference of the entire lake. This lake is managed as a

two-story lake, meaning that the epilimnion and metalimnion zone provides suitable

habitat and nutrients for gamefish such as bass and panfish, while the hypolimnion zone

provides habitat and nutrient requirements for fish such as trout.

Bear Lake is specifically a kettle lake. When a glacier is retreating in the glacial

outwash plain, large blocks of ice are left behind that form a depression, and if below

the water table, a kettle lake is formed such as Bear Lake.The topography surrounding

Bear Lake is hilly, mostly forested, with predominantly sandy soils. The southeast corner

of Bear Lake provides public access with a paved launch ramp, and parking for a few

vehicles with trailers.

Bear Lake is fairly round and of uniform shape with no inlets or outlets. However,

it does have a small, shallow connected “pond” named Elanor Bay on the southwest

corner, as seen in Figure 1, several acres in size that at its deepest point is only 1 to 1.2

meters deep. With only 16 per cent of the waters shallower than 2 meters, Bear Lake

has a small littoral zone that borders the edge of the lake, and an extensive limnetic

zone with 45% of the lake being deeper than 6 meters as seen in Figure 2. In these

zones, the light does not penetrate to the bottom for plant growth.

We were asked by the Bear Lake Association to perform a shoreline assessment

and advise accordingly. The assessment, sampling and data collecting were performed

on Tuesday July 23rd and Thursday July 25th. Due to the wind and the instability of the

boat, confidence in the accuracy of the data collected on July 23 is limited, and

therefore will not be included. On July 25th, the wind speed was only 4 mph and with

the air temperature of 27°C, the weather allowed for better data collection. It was

Figure 1: Bathymetric map of Bear Lake (Source: Lake maps of Kalkaska County)

approximately 25% cloudy at 14:00, the time of sampling Bear lake. This report is on the

current condition of Bear Lake by the 2019 limnology class taught by Dr. John Korstad.

Figure 2: Satellite map of Bear Lake (Source: google maps)

Materials and Methods

Our class sampled Bear Lake using resident Sam Rahaim’s pontoon boat. We

also completed a shoreline assessment, assessing the vegetation and seawall per cent

cover, and shore angle around the entire lake.

Temperature of Water: Thermal Stratification and Lake Turnover

Thermal stratification is a phenomenon that causes the waters to form distinct

layers as a result of sunlight that penetrates the surface waters. The density of water is

dependent on its temperature. The colder the water, the higher density it is. Conversely,

the warmer the water, the less dense it becomes. Water density affects the mixing of the

waters because the greater the difference in density, the more unlikely the water layers

will mix. As a result, the lake “stratifies,” typically forming three different layers and is

known as thermal stratification.

The layer closest to the surface, called the epilimnion, readily receives the sunlight, is

the warmest and has the least dense waters. The deepest layer at the bottom of the

lake, known as the hypolimnion, is the coldest and has the most dense waters. The

middle layer, or metalimnion, is the transition zone between the warm waters of the

epilimnion and the cool waters of the hypolimnion. Within the metalimnion, at the point

of the greatest temperature and density differences, is the thermocline. In this zone the

temperature decreases an average of 1° Celsius per meter.

In areas that experience seasonal temperature differences, such as northern

Michigan, lakes often undergo a turnover. As the surface waters begin to cool they

become denser, causing the epilimnion to extends down towards the hypolimnion,

weakening the thermocline so that mixing between the layers becomes easier. The

mixing occurs until the entire lake is the same temperature, known as isothermal, and

allows lake turnover to occur. In lakes like Bear Lake, in climates such as northern

Michigan, Lake turnover occurs twice a year; in the fall and the spring.

Transparency of Water (Secchi Depth) and Trophic State Index

The Secchi disk is used to

measure relative transparency of the

water. It is lowered into the water until

it is no longer visible from the surface

and the depth at which this point

occurs is recorded. This test gives an

idea of the particulate matter, mainly

phytoplankton in the water. If the

Secchi depth is between 8-40m it is

considered to be an oligotrophic lake

due to low levels of nutrients leading to low phytoplankton present in the lake. Likewise,

if visibility is between 0.1-2 it is considered a eutrophic lake due to much higher levels of

nutrients. Resulting in higher algal growth and therefore higher turbidity of water.

The Trophic State Index (TSI) is a classification system that rates a waterbody

based on the biological productivity that occurs in the water. The TSI quantifies water

quality using the Secchi depth, chlorophyll-a concentrations (algal biomass), and total

Figure 3: Secchi Disk (Source: schoolspecialty.com)

phosphorus level on a scale between 0 and 100, shown in Table 1. For this report

however only Secchi depth was used to calculate TSI.

Dissolved Oxygen and Temperature YSI Electronic Probe

Dissolved oxygen (DO) is naturally 10,000 times more concentrated in air than

water. Oxygen dissolves into water in one of two ways: physically at the surface air

mixes with water, and biologically when aquatic

plants undergo photosynthesis. The level of DO

required by aquatic animals varies, but a value

of at least 5.0 ppm is desirable for most aquatic

organisms.

Table 1: Trophic State IndexSource: Lake Access, www.lakeaccess.org/lakedata/

DO decreases with rising temperature, so values are expected to be higher in

winter and lower in the summer. DO also usually

decreases with depth so surface DO values are

higher than at the bottom of the lake. The DO in

lakes and ponds with high nutrient concentration can change

dramatically throughout the day because of photosynthesis.

YSI electronic probe was used to measure the dissolved

oxygen content and temperature in degrees Celsius was

recorded at every meter from the surface to the bottom.

Dissolved oxygen is measured in units of parts per million

(ppm).

Light

Light penetration was measured every meter of depth from the surface to the

bottom. A protomatic light photometer was used (Figure 6). This is another way to

assess whether the lake is oligotrophic or eutrophic based on the amount of

phytoplankton in the water.

Figure 4: Dissolved Oxygen Tolerance Source: PBS.com

Figure 5: YSI Electronic Probe Source: nclabs.com

Figure 6: Protomatic light photometer Source: ebay.com

Alkalinity & Hardness

Alkalinity is the measurement of the water’s ability to resist changes in pH. If a

lake has low alkalinity it is more susceptible to rapid changes in pH when acids or bases

enter the water. Using a Van Dorn Bottle Sampler (Figure 7), we collected water from

the bottom of the lake. A Hach titration kit (Figure 8) was used to test water samples

from both the surface and bottom of the lake.

Hardness

Hardness is a measure of the amount of Calcium and Magnesium ions in water

which results mainly through the weathering of rocks. Limestone is a natural source of

hardness; which interestingly enough the bedrock in this area of North America was

Figure 7: Van Dorn Bottle Sampler Source: ecoenvironmental.com

Figure 8: Hach Titration kit Source: hach.com

previously coral reefs. Its chemical name is

calcium carbonate (CaCO3), or magnesium

carbonate (MgCO3).

Dissolved limestone is an important

feature of healthy lakes, but too much calcium

or magnesium ions not only makes the water “hard”, leading to scaly deposits, but it can

also lower fish reproduction. Most fish and aquatic organisms live in water hardness

between 15 and 200 mg/L Table 2. Hardness was performed with the Hach titration kit

(Figure 8) with surface and bottom water being tested.

pH, Conductivity, & Redox Potential

The pH of a lake can change throughout the season and sometimes even daily.

The pH is affected by atmospheric carbon dioxide

(CO2) because CO2 in water forms a weak acid

known as carbonic acid. The optimal pH range

for healthy aquatic life is between 6.0 and 8.5. A

pH that is higher than 11 or lower than 4 is lethal

to fish and most aquatic life.

Monitoring pH levels of a lake after a heavy rain can

inform homeowners about potential runoff issues. Vernier GoDirect Wireless Probes

Table 2: Water Hardness as CaCO3

0 - 20 mg/L soft

21 - 60 mg/L Moderately soft

61 - 120 mg/L Moderately hard

121 - 180 mg/L Hard

More than 181 mg/L Very Hard

Source: Water Chemistry Monitoring. 6th ed., Alabama Water Watch Association, 2018.

Figure 10: Wireless Probe Source: vernier.com

(Figure 10) was used to calculate pH, Conductivity, and Redox Potential of surface and

bottom water in the lake.

Plankton Samples

The diversity and abundance, or lack of zooplankton

and phytoplankton can inform us about the health of a

lake. An 80µm mesh plankton net (Figure 12) was used

to collect samples of zooplankton and phytoplankton

from the lake. The net was lowered three times from the

surface to the bottom to obtain a dense sample that was

later preserved and identified using a microscope in the lab.

Table 3: Effects of pH on Fish and Other Aquatic Life

pH Effects

Higher than 11 Alkaline death point

9.0 - 11.0 Slow growth and limited production

6.0 - 8.5 Optimum range

4.0 - 5.5 Slow growth, no reproduction in many species

Under 4.0 Acid death point

Figure 12: Plankton net Source: sciencefirst.com

Source: coastadapt.com

Coliform Bacteria

We used Coliform Easygel and a pipet at each of the 10 sites. The test was done

twice at each site for a total of 20 tests. Sites were selected by the Bear Lake

Association representatives for three reasons: to ensure older septic tanks were intact

and not releasing coliform bacteria; as advised by limnologist, excessive/new aquatic

plant growth. Following the Coliscan Easygel kit directions, we sampled 3 ml of water

from each site and took the sample back to the lab to put them in Petri dishes and

placed them in an incubator at 37

degrees Celsius for 30 hours.

Benthic Sample

Benthos were collected using an Ekman Dredge (Figure 14) lowered to the

bottom of the lake. The sample was placed in a sieve bucket in order to examine

organisms collected from the benthic zone. The amount of organisms present in this

sample gives us a good idea of the amount of dissolved oxygen present at the bottom of

the lake.

Figure 13: Bacteria petri dish Source: biodesign.com

Shoreline Analysis

The rate at which erosion of your shoreline occurs depends on a number of

factors, including:

• Height and composition - such as silt, sand, gravel, and boulders.

• Amount and type of vegetation

• Groundwater movement and drainage patterns

As seen in this diagram from the Environmental Protection Agency (EPA).

Figure 14: Ekman Dredge Source: forestry-suppliers.com

Figure 19: “EROSION ON BLUFFS.”Source: EPA

As waves erode the bottom of lakeshore bluffs they loosen the soil, washing it

away. Additionally, increased groundwater movement from road and roof runoff, septic

drains, rain and irrigation increase the saturation of the soil.

Vegetation along the shoreline mitigates erosion because root systems hold soil in

place. Vegetation, such as native plants, and drift logs help dissipate wave energy,

mimicking nature and protecting property.

Not only are steep slopes, or bluffs, at a larger risk of erosion, but they also are

at risk of sudden landslide or collapse. This is because as the wave hits the shoreline, it

“licks” out the soil beneath the surface of the water, leading to an unstabilized bank that

eventually collapses into the water.

Ground Water Movement and Drainage

Land development, can increase the intensity and effects of runoff. Surfaces

such as roads, roofs, driveways and grass all increase the amount of water runoff that

would otherwise penetrate the ground. Nutrients, pollutants and sediments that were on

the surface are picked up in the runoff and carried into the lake, each adding to the

particulates and overall concentration of the various “contaminants.” In this way, runoff

is the number one process of cultural eutrophication, and something that should be

managed closely.

Results

Temperature with Depth

Figure 15 shows the characteristic summer lake temperature of a thermally

stratified lake. The temperature gradually decreases in the upper waters of the

epilimnion. At about 3 meters deep, the water temperature decreases much more

rapidly until about 10 meters deep, this zone of transition zone in the metalimnion

layer is known as the thermocline. This is an expected response of a healthy lake

and is a function of the temperature and densities of the water. Because the lake

is not undergoing a mixing in the summer this gives evidence that this lake is

undergoing thermal stratification.

Dissolved Oxygen with Depth

The dissolved oxygen vs depth graph (Figure 16) shows the average content of

DO at given measured depths of the lake. In the epilimnion, from the surface to about 2

meters DO levels are just below 10 ppm. The DO content then suddenly rises at 4

meters until 11 meters of depth. At 12 meters of depth the DO levels begin to drop until

they level out at 11 ppm. The DO levels are above the minimum levels in each zone and

well within the healthy range of supporting an abundant amount of life. Due to its very

low

nutrient

level,

Bear

Lake is

able to

maintain

dissolved

oxygen throughout most of the water column for the entire summer. Only in the very

deep waters does the dissolved oxygen become low.

Light Penetration with Depth

As we lowered the protomatic light photometer every meter starting at the

surface light penetration decreased as evident in our graph (Figure 17), which is not

surprising because most lakes are this way due to nutrients and other elements limiting

light penetration.

Chemical Data

According to Table 4 below, Bear Lake has an average alkalinity and hardness

for an oligotrophic lake. Hardness is higher at the bottom compared to the top because

it is groundwater fed like most lake in this area of Northern Michigan. Alkalinity

decreases at the bottom compared to the surface because calcium precipitates toward

the bottom. Conductivity is higher at the bottom because of dissolved calcium ions that

originate from weathering of rocks which are found at the lakebed. Redox potential is

lower at the bottom of the lake because there is less dissolved oxygen in the benthic

zone.

Shoreline Analysis

The shoreline angle, seawall and percent vegetation can be seen in Table 5,

below. In the analysis of the shoreline survey, it can be evident that there is a wide

variation of bank slopes, vegetation, and run off, with a large percentage of the

shoreline area having a slope over 75°. Natural vegetation is important in limiting

Data collected on July 25, 2019, from Lake Ecology 330

erosion of the shoreline. Examples of this can be seen along the shoreline in areas with

vegetation compared to areas without vegetation.

Plankton

Plankton that was collected from Bear Lake included genus Ceratium,

Staurastrum, Diaptomus, Gleocapso, Aphanocapsa, Ceeosphaerium, Oedogonium and

Polyarthra. Although a benthic sample was collected, we did not identify any benthos.

�

Asterionella Source: shetlandlochs.com

� Staurastrum Source: http://oceandatacenter.ucsc.edu

!

Diaptomus Source: Coinme

�

Ceratium Source: Algal Web

! Aphanocapsa Source: Protist information server

! Gleocapso Source: PhycoKey

! Oedogonium Source: AlgalWeb

! Polyarthra Source: Protist information server

Coliform Bacteria

A summary of the bacteria data are included in Table 6 below. There were no

fecal coliforms found in any of the 20 samples of taken from Bear Lake. Very few non-

fecal coliforms were found in the samples, no more than 1 coliform, except for the public

access site.

Trophic State Index (TSI)

The Trophic State Index using the Secchi disk depth was calculated to be 37;

using the formula: 60 - [14.41 * ln(5.0)]= 36.81. This TSI indicates that Bear Lake is an

oligotrophic lake, meaning it is good water quality with low biological productivity

because of low nutrient content.

Recommendations and Conclusion

Bear Lake has shown to be a healthy oligotrophic lake after our sampling and

data interpretation. With no identification of fecal coliforms the Bear Lake residents

seem to be practicing good septic tank management strategies, and should continue to

monitor and update them as needed in the future. The highest level of Non-fecal

coliforms was 233 CFU/100mL, and was found at the public beach access. At 233

CFU/100mL, Bear Lake is performing exceptionally well.

There was a relatively high level of plankton diversity. This could suggest that the

aquatic ecosystem is in a healthy equilibrium. However, it should be noted that there

were increased numbers of bluegreen algae. Because an abundant amount of

bluegreen algae is an indicator eutrophication, this should be closely monitored. Bear

Lake is well within a healthy range of bluegreen algae; however, moving forward it will

be important to continue to monitor. If increasing trends of bluegreen algae is noted it is

important to take action. Having an action plan ready ahead of time is a good idea.

Often, the most common reason for bluegreen algae growth is increased nutrients

(usually phosphorus) so a good place to start an effective action is to communicate to

the homeowners to be aware of their nutrient inputs. Encourage everyone who lives

around the lake to not fertilize their lawns, or at least use non-P fertilizers; do not use

garbage disposals; have septic tanks/fields inspected and upgraded as often as

possible; mulch ‘green’ waste and use that to place around yard plants; use lake water

to irrigate lawns and flowers; keep the littoral zone (nearshore aquatic plants like cattail)

‘healthy’ by protecting existing plants, adding more plants, etc. All of these actions add

up and contribute to the over all health of your lake.

In conversation with home owners and lake association members from the area,

the water level is higher than it has been in approximately 50 years, and levels are still

rising. If this trend continues, bank erosion and sedimentation will continue. As a result,

water quality could be negatively affected. Therefore, it is important to implement

shoreline management plans to reduce the probability and rate of occurrence. The

recommendations given here are by no means exhaustive; a much more thorough

shoreline examination would be needed.

One of the best ways to protect your lake is to protect your shoreline. And one of

the best ways to protect your shoreline, whenever possible, is to leave it in its natural

state. If that is not possible, naturalization with native plantings, log berms/fallen dead

trees and other natural wake protections as seen in this picture below.

Residents living on Bear Lake need to be encouraged to not remove natural

vegetation from their property, particularly at the shoreline, as this removal of a buffer

zone will increase the rate of erosion and eventually harm the ecosystem of the lake.

Planting native aquatic plants at the shoreline can help filter the runoff and acts to clean

the water.

As a waterfront property owner, you are the steward of your own special piece of

Bear Lake. By naturalizing your shoreline where possible, you can help maintain the

survival of native fish and wildlife. Protecting your property from erosion and cultural

eutrophication is feasible, affordable and a smart investment for Bear Lake’s future. In

conclusion, Bear Lake is in good condition and the continuation of management

strategies will ensure a stable and healthy lake for the residence to enjoy!

Figure 18. Source: Shore Friendly

Works Cited

1. LD - Data Info TSI, www.lakeaccess.org/lakedata/datainfotsi.html.

2. “Home.” Global Water Watch, www.globalwaterwatch.org/.

3. “Shoreline Erosion.” Michigan Inland Lake Shorelines, www.shoreline.msu.edu/ shorelinemgt/erosion/.

4. “EROSION ON BLUFFS.” Shore Friendly, www.shorefriendly.org/your-erosion- risk/ on-bluffs/.

5. Water Chemistry Monitoring. 6th ed., Alabama Water Watch Association, 2018.

6. Bacteriological Monitoring. 3rd ed., Alabama Water Watch Program, 2012.

7. Tonello, Mark. Bear Lake. Michigan Department of Natural Resources Status of the Fishery Resource Report. 2015

8. “Trophic State Index.” Lake Access, www.lakeaccess.org/lakedata/datainfotsi.html.